Systems and Methods for Improving Penetration of Radiographic Scanners

ABSTRACT

Systems and methods are used to increase the penetration and reduce the exclusion zone of radiographic systems. An X-ray detection method irradiates an object with X-ray fanlets including vertically moving fan beams, each fanlet having an angular range smaller than the angular coverage of the object. The fanlets are produced by modulating an X-ray beam, synchronizing the X-ray beam and the fanlets, detecting the fanlets irradiating the object, collecting image slices from the detector array corresponding to a complete scan cycle of the fanlets, and processing the image slices collected for combining into a composite image.

CROSS-REFERENCE

The present specification relies on, for priority, U.S. PatentProvisional Application No. 62/362,585, entitled “Systems and Methodsfor Improving Penetration of Radiographic Scanners”, and filed on Jul.14, 2016.

The above-mentioned applications are herein incorporated by reference intheir entirety.

FIELD

The present specification is related to radiographic systems. Morespecifically the present specification is related to a method ofincreasing penetration of radiographic systems and reducing exclusionzones.

BACKGROUND

X-ray imaging is one of the most common methods used for detectingcontraband in cargo. However, during the inspection of large containers,as a result of inadequate penetration by the radiation, it is common fortraditional X-ray systems to produce images with dark areas. These darkareas might be indicative of the presence of threat materials; however,they yield little information about the exact nature of threat. Typicalpenetration depths of existing cargo inspection systems range between200 and 400 mm of iron.

While it is known that systems with higher penetration can be obtainedwith high-power sources, using a higher power source increases the sizeand footprint of the radiation exclusion zone, limiting wide deploymentof such systems. Thus, the use of high-energy X-rays for cargoinspection is not without some tradeoff. On one hand, the source needsto produce high-intensity, high-energy X-ray beams in order to providehigh imaging penetration of the cargo. On the other hand, higher X-rayintensities/energies lead to larger radiation footprint, requiring alarger controlled area (exclusion zone), or more shielding around thesystem. This may also lead to higher radiation dosage to cargo, and inthe case of portal systems, to the driver of the cargo as well.

When the exclusion zone is not limited or a shielded building isprovided to limit the size of the system, the increase of penetrationdepth begins to taper down as the source intensity is increased, untilit reaches a point when larger intensities of the X-ray source do notcause an increase in the penetration depth of the X-rays. The maineffect that limits the highest achievable penetration depth is scatter,which represents a background added to the transmitted signal. X-raysfrom the shaped fan beam scatter from the container walls and cargo andproduce a low-frequency background that adds to the transmitted image,effectively reducing contrast, thereby limiting penetration. Theintensity of the scatter depends on the number of X-rays impinging onthe object being scanned. Longer and wider fan beams produce morescatter than shorter and narrower fans, approximately proportional tothe ratio of the irradiation areas. The transmitted signal received atthe detectors is thus polluted from X-rays scattering from other partsof the object being inspected. Hence, there is a need to reduce thescatter further to increase X-ray penetration.

The most common approach to reduce scatter is to use collimators inconjunction with the detectors. However, deep, heavy and expensivecollimators are needed for obtaining desired penetration. In addition,the scatter rejection is only reduced partially, as a collimator itselfbecomes a source of scatter.

Other existing methods to reduce the measured scatter radiation consistof employing Cerenkov detectors that intrinsically are not sensitive tolow-energy X-rays, which is characteristic of the scatter radiation.However, these Cerenkov and energy-sensitive detectors are more complexand expensive than standard X-ray detectors and typically do not enableimproved intensity modulation. Also, when the source intensity isincreased, these detectors start saturating due to the very high countrate. Still other methods are based on measuring the energy spectrum ofthe radiation and removing the low-energy signals.

Currently available X-ray sources usually have a single fixed intensitysetting that is set to the output level requested by the customer, whichis typically the highest setting that still complies with a requiredradiation footprint. Moreover, during a typical scan, source output isoften much higher than needed to achieve sufficient imaging penetration;not just from one vehicle or container to the next, but also within thecargo of the same vehicle or container. Hence, there is a need toincrease X-ray intensity in order to increase penetration withoutincreasing the exclusion zone and/or radiation dosage.

Current methods for increasing penetration are based on beam-modulatingintensity based on the highest attenuation measured in the previousslice. However, the beam intensity along the slice may be higher thanrequired due to the high attenuation of a small area of the object. Thehigher intensity results in a larger exclusion zone, or if limited, in areduction of the source strength that results in lower penetration.

PCT Publication Number WO2011095810A3, assigned to the Applicant of thepresent specification discloses “[a] scanner system comprising aradiation generator arranged to generate radiation to irradiate anobject, detection means arranged to detect the radiation after it hasinteracted with the object and generate a sequence of detector data setsas the object is moved relative to the generator, and processing meansarranged to process each of the detector data sets thereby to generate acontrol output arranged to control the radiation generator to vary itsradiation output as the object is scanned.” There is still a need,however, for more fine control to modulate the intensity as a functionof vertical positions within the slice to further optimize the intensityimparted to the object. The WO2011095810 publication is incorporatedherein by reference in its entirety.

In addition, U.S. Pat. No. 9,218,933, also assigned to the Applicant ofthe present specification, discloses “[a]n X-ray source for scanning anobject comprising: an electron beam generator, wherein said electronbeam generator generates an electron beam; an accelerator foraccelerating said electron beam in a first direction; and, a first setof magnetic elements for transporting said electron beam into a magneticfield created by a second set of magnetic elements, wherein the magneticfield created by said second set of magnetic elements causes saidelectron beam to strike a target such that the target substantially onlygenerates X-rays focused toward a high density area in the scannedobject”. What is still needed, however, is a system that does notrequire complex electron-transport components. The '933 patent isincorporated herein by reference in its entirety.

Even when a system has very high penetration, there may be dark alarmsthat require labor-intensive manual inspection for clearing. There is aneed for reducing the dark alarm rate further to reduce manualinspections.

Therefore, there is a need for scanning systems with increasedpenetration and smaller exclusion zones, resulting in improvedperformance and lower alarm rates and easy deployment in a wide range ofenvironments.

SUMMARY

In some embodiments, the present specification discloses an X-raydetection system with increased penetration comprising: an X-ray sourcefor projecting an X-ray beam towards an object; a mechanism forproducing one or more fanlets from the X-ray beam, each fanletcomprising a vertically moving fan beam having an angular range smallerthan the angular coverage of the object; a detector array for detectingthe fanlets projected on the object; a controller for synchronizing theX-ray source and the mechanism, and collecting image slices from thedetector array corresponding to the fanlets; and a processing unit forcombining the image slices collected into a composite image.

In some embodiments, the present specification discloses an X-raydetection system configured to provide for increased penetration of anobject, comprising: an X-ray source for generating an X-ray beam in aninspection volume; a conveyor for moving the object through theinspection volume; a collimator positioned between the X-ray source andthe object, wherein the collimator is configured to receive the X-raybeam and produce one or more fanlets from the X-ray beam, wherein eachfanlet comprises a vertically moving fan beam having an angular rangegreater than 1 degree but smaller than the angular coverage of theobject; a detector array opposing said X-ray source and positionedwithin the inspection volume for detecting the one or more fanletsprojected on the object; a controller configured to synchronize theX-ray source and the collimator and collect image slices from thedetector array corresponding to each of the one more fanlets; and aprocessing unit for combining the image slices collected into acomposite image.

Optionally, the X-ray source is a pulsed X-ray source.

Optionally, the X-ray source produces dual-energy beams. Stilloptionally, the dual-energy beams are interlaced.

Optionally, the X-ray source produces X-ray pulses comprising low andhigh energy X-ray beams separated in time.

Optionally, the controller is configured to control the conveyor suchthat a total time for the one or more fanlets multiplied by a rate ofspeed of the conveyor is equal to or less than a width of a detector inthe detector array.

Optionally, the collimator is configured to generate an overlap betweenthe one or more fanlets of approximately 1 degree with respect to theobject.

Optionally, the X-ray source is a CW X-ray source.

Optionally, the collimator for producing the one or more fanletscomprises a plurality of controlled fast actuators coupled with beamattenuators to shape the X-ray beam.

Optionally, the collimator for producing the one or more fanletscomprises a beam chopper.

Optionally, the collimator for producing the one or more fanletscomprises a rotating wheel with slits designed to produce the verticallymoving one or more fanlets.

In some embodiments, the present specification is directed toward anX-ray detection method comprising: irradiating an object with more thanone X-ray fanlet, wherein each X-ray fanlet comprises a verticallymoving fan beam having an angular range greater than 1 degree butsmaller than the angular coverage of the object and wherein each X-rayfanlet is produced by using a collimator for collimating an X-ray beamgenerated by an X-ray source; synchronizing the X-ray beam and the morethan one fanlet; detecting the more than one fanlet irradiating theobject; collecting image slices from the detector array corresponding toa complete scan cycle of the more than one fanlet; and processing theimage slices and combining the image slices into a composite image.

Optionally, the method further comprises adjusting a beam intensity andenergy of each of the more than one fanlets based on signals detectedfrom a previous fanlet at a same vertical position with respect to theobject to generate a control output, wherein the control output is usedto control the X-ray detection method.

Optionally, the X-ray source is a pulsed X-ray source.

Optionally, the X-ray source produces dual-energy beams.

Optionally, the dual-energy beams are interlaced.

Optionally, the X-ray source produces X-ray pulses comprising low andhigh energy X-ray beams separated in time.

Optionally, the collimator is configured to generate an overlap betweenthe one or more fanlets at every position with respect to a surface areaof the object.

Optionally, the collimator comprises a spinning cylinder with a helicalaperture.

Optionally, the collimator comprises a plurality of controlled fastactuators coupled with beam attenuators to shape the X-ray beam.

Optionally, an energy of each of the more than one fanlet is adjusted ata same fanlet location in a following cycle to allow for interlaceddual-energy scanning of every vertical position.

Optionally, the X-ray source is a CW X-ray source.

In some embodiments, the present specification discloses a method foroperating a scanning system, wherein said scanning system comprises anX-ray source, an array of detectors, and a processor to process andanalyze image data, the method comprising: generating a first X-ray beamin order to conduct a first scan to produce an image of the object beingscanned; determining areas in said image data that require a moredetailed inspection; configuring a collimator to limit a second X-raybeam such that, upon emission of the second X-ray beam, the collimatoremits a plurality of fanlets, wherein each fanlet has an angular rangethat is less than an angular range covering an object but greater than 1degree; and moving the object relative to the X-ray source and the arrayof detectors to perform a second scan on the areas.

Optionally, said areas represent a lack of penetration by the firstX-ray beam during said first scan.

Optionally, said areas represent items of interest or alarm such asexplosive, firearms, drugs or contraband.

Optionally, the X-ray source and array of detectors are mounted on agantry.

Optionally, the collimator comprises a plurality of controlled actuatorscoupled with beam attenuators to shape the second X-ray beam.

Optionally, the collimator comprises two vertically controlledattenuators to inspect only said areas.

Optionally, a scan of said areas using said plurality of fanlets isperformed at a lower speed compared to a speed of a scan using the firstX-ray beam.

Optionally, the method further comprises replacing the areas generatedby a scan using a first X-ray beam with images of the areas generated bya scan using the plurality of fanlets.

The aforementioned and other embodiments of the present shall bedescribed in greater depth in the drawings and detailed descriptionprovided below.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the present specificationwill be further appreciated, as they become better understood byreference to the detailed description when considered in connection withthe accompanying drawings:

FIG. 1A illustrates a conventional X-ray system for scanning cargoshowing a plurality of possible X-ray paths;

FIG. 1B illustrates an exemplary detector, with a collimator, showing aplurality of possible X-ray paths;

FIG. 2 illustrates a system comprising pulsed-source projectingvertically-moving fanlets for scanning cargo resulting in reducedscatter, in accordance with an embodiment of the present specification;

FIG. 3 illustrates a system comprising a continuous wave (CW) sourceprojecting vertically continuously-moving fanlets to scan a cargoresulting in reduced scatter, in accordance with another embodiment ofthe present specification;

FIG. 4 is an exemplary illustration in which the imaging system of thepresent specification is used for scanning a standard penetrationphantom object;

FIG. 5 illustrates exemplary simulated images for standard penetrationphantom objects obtained with a full fan beam of X-rays and multiplefanlets via the imaging system described in FIG. 4, in accordance withan embodiment of the present specification;

FIG. 6A illustrates a mechanism comprising multiple actuators connectedto beam attenuators to produce vertically-moved fanlets, in accordancewith a preferred embodiment of the present specification;

FIG. 6B is a block diagram illustrating various attenuatorconfigurations within the mechanism for producing thevertically-translated fanlets shown in FIG. 6A, in accordance with apreferred embodiment of the present specification;

FIG. 7 illustrates an exemplary design of a spin-roll chopper used formoving X-ray fanlets vertically with respect to an object being scanned,in accordance with an alternate embodiment of the present specification;

FIG. 8A illustrates an exemplary mechanism for generating movingfanlets, in a first position, according to an alternate embodiment ofthe present specification;

FIG. 8B illustrates an exemplary mechanism for generating movingfanlets, in a second position, according to an alternate embodiment ofthe present specification;

FIG. 8C illustrates an exemplary mechanism for generating movingfanlets, in a third position, according to an alternate embodiment ofthe present specification;

FIG. 8D illustrates an exemplary mechanism for generating movingfanlets, in a fourth position, according to an alternate embodiment ofthe present specification; and,

FIG. 9 is a flow chart that describes scanning steps of the imagingsystem of the present specification, in accordance with embodiments.

DETAILED DESCRIPTION

The present specification describes scanning systems having increasedpenetration capability and smaller exclusion zones, resulting inimproved performance and easy deployment in a wide range ofenvironments. Embodiments of the present specification are well-suitedfor applications in environments including, but not limited to,container, truck and railcar inspection. Some embodiments of the presentspecification are particularly well-suited for use in inspectingslow-moving vehicles.

The present specification is directed towards systems and methods forboth reducing the exclusion zone and increasing the penetrationcapability of radiographic systems, such as X-ray scanners. In anembodiment, the imaging system described in the present specificationenables the scanning of high density cargo with a sufficient penetrationdepth for the detection of contraband resulting in a low probability ofdark alarms that may require a secondary inspection. The presentspecification also describes an imaging system having a lower impactfrom scatter radiation that is observed in conventional X-ray scannersand that can be used for inspecting high-density cargo. The presentspecification also describes a novel method that allows for optimizationof the radiation intensity imparted to cargo and environment, whichfurther increases penetration.

In an embodiment, the present specification describes a novel mechanismfor reducing scatter by producing a vertically moving fan beam with anangular range smaller than the angular coverage of the object beingscanned. The present specification provides a vertically moving fan beamor “fanlet” synchronized with a pulsed X-ray source and a dataacquisition system. In an embodiment, the “fanlet” represents a portionof the total overall fan beam, and is vertically translated to cover theextent of the object.

In an embodiment, a vertical collimator projects a fanlet having anangular range smaller than the angular coverage of the object beingscanned. In an embodiment, the angular range is achieved by using acollimator having dimensional characteristics that are independent ofthe object, but that are tailored to insure the highest and widestpossible object dimensions are accounted for. In an embodiment, thecollimator is designed to provide collimation for a predefined objectheight and object width, which are larger than a standard object heightand width, thereby insuring no portion of the object remains unscanned.

The fanlet, via collimator mechanics, is translated vertically to coverthe angular spread of the object. A pulsed linac X-ray source and a dataacquisition system are synchronized with the moving collimator in such away that the image of the object is acquired at intervals, where in onecycle the fanlets cover a slice of the object with no gaps and,optionally, a minimal overlap. The image from each fanlet is thencombined to produce a slice image. In one embodiment, to minimize theeffect of object motion, the source pulsing frequency is increased bythe number of fanlets. The advantage of this embodiment is that thescatter is reduced as the irradiated area is reduced in eachacquisition.

The present specification is also directed towards reducing theradiation exclusion zone. In additional embodiments, the signals fromeach fanlet are used to control the intensity of the fanlet for thefollowing cycle, to optimize the source intensity. In an embodiment, thebeam intensity and/or energy is modulated based on the transmissionobserved in each fanlet to expose the object to the minimum intensityrequired for penetration, while at the same time reducing the dose tocargo and the environment resulting in a smaller exclusion zone. This issimilar to the intensity modulation described in PCT Publication NumberWO 2011095810A, incorporated herein by reference in its entirety, whichis applied to the full fan beam.

The embodiments described herein may be employed for dual-energyscanning as well, since the time between pulses at the same verticallocation is the same as in a standard system because the pulsing rate isincreased accordingly. However, for fast moving objects, the pulsingfrequency is high and it might not be possible to increase the pulsingfrequency by a factor of two or three. In these applications, thepreferred embodiment is to use a pulsed source, where each pulsecontains dual energies separated by a short time.

In another embodiment, a Continuous Wave (CW) source is used. In thisembodiment, the data acquisition system collects data continuously at aplurality of time intervals with times shorter than the time it takesfor the collimator to move from the top position to the bottom positionto cover the slice.

The present specification is directed towards multiple embodiments. Thefollowing disclosure is provided in order to enable a person havingordinary skill in the art to practice the specification. Language usedin this specification should not be interpreted as a general disavowalof any one specific embodiment or used to limit the claims beyond themeaning of the terms used therein. The general principles defined hereinmay be applied to other embodiments and applications without departingfrom the spirit and scope of the specification. Also, the terminologyand phraseology used is for the purpose of describing exemplaryembodiments and should not be considered limiting. Thus, the presentspecification is to be accorded the widest scope encompassing numerousalternatives, modifications and equivalents consistent with theprinciples and features disclosed. For purpose of clarity, detailsrelating to technical material that is known in the technical fieldsrelated to the specification have not been described in detail so as notto unnecessarily obscure the present specification.

It should be noted herein that any feature or component described inassociation with a specific embodiment may be used and implemented withany other embodiment unless clearly indicated otherwise.

FIG. 1A illustrates an X-ray system comprising an X-ray source 110 and adetector array 120 scanning a railcar 130 containing cargo 140. X-raypath 150 represents the non-interacting X-rays that are transmittedthrough the cargo 140. In an ideal system, these would be the onlyX-rays that would be detected. X-ray paths 160 represent X-raysscattered by the walls of the railcar container 130, and X-ray paths 170represent X-rays scattered within the cargo 140. The scattered X-raysrepresented by paths 170 constitute background noise for the X-raysystem. In various embodiments, the present specification providessystems and methods to reduce the background noise.

FIG. 1B illustrates a collimator coupled with a detector array forreducing the X-ray scatter signal. In FIG. 1B a detector collimator 180is coupled with the array of X-ray detectors 120 for reducing thescattered X-rays (such as X-rays 170 shown in FIG. 1A). As shown, thepath of the primary X-ray beam 190 does not interact with the collimator180 and is detected by the detector array 120, while X-rays followingpath 192 are absorbed in the collimator 180 and not detected. Also,X-rays following path 194 go through collimator 180 and are detected bydetector array 120, while X-rays following path 196 scatter incollimator 180 into the detector array 120 and are also detected.

These effects show that collimators reduce scatter, however, deepercollimators, or collimators that have a longer source to detectordistance, result in higher rejection. The performance of the collimatoris affected by the ratio of length to width of the individual collimatoropenings. The higher the ratio of length to width, the better thescatter rejection of the collimator; however, such an embodiment is moreexpensive to manufacture.

Further, as the collimator is made deeper, scatter in the collimatorlimits the rejection. Thus, there is a trade-off between using a deepcollimator and achieving scatter reduction as the X-rays that scatter inthe collimator (which is used to reduce scatter from the cargo) maybecome greater in number than the left-over scatter from the cargo. Inan embodiment, collimator depth is maximized at 300 mm, after whichdepth, gain is minimized. It should be noted that the collimator wallthickness cannot be made too thick as it would reduce the number ofunscattered X-rays. Thus, in order to reduce X-ray scatter, a greaternumber of collimator panes is employed.

The present specification, in an embodiment, provides a method ofreducing X-ray scatter signal by generation of a vertically moving X-raybeam or fanlets. FIG. 2 illustrates a system comprising a pulsed sourceprojecting vertically-moving fanlets to scan a cargo with reducedscatter, in accordance with an embodiment of the present specification.The system comprises a pulsed X-ray source 210 for scanning a railcar(or other object) 230 and a detector array 220. Examples of suitableX-ray sources include, but are not limited to, electron linac hitting atungsten target and CW sources such as Rhodotron and superconductinglinac. One of ordinary skill in the art would appreciate that any pulsedX-ray source known in the art may be employed. Collimator 240 representsa mechanism that produces a vertically moving fan beam or fanlets 250,260 and 270, with an angular range smaller than the angular coverage ofthe railcar 230.

Referring back to FIG. 2, the signal produced by fanlet 260 has reducedscatter compared to the full fan-shaped X-ray beam that is generallyused to inspect cargo in conventional systems. In an embodiment, theX-ray pulses and the scanning mechanism are synchronized to collect datawhen the fan beam(s) are projected to fanlet positions 250, 260 and 270to cover the vertical extent of the cargo railcar 230 in one cycle. Aprocessing unit combines the data from the fanlets 250, 260, 270 to forman image of a slice of the cargo railcar 230. As the collimator definesthe fanlet and tends to produce a beam with fuzzy edges, a small overlapbetween the fanlets 250, 260, 270 is preferred to allow for better“stitching” of the fanlets 250, 260, 270 into a slice image to eliminateor minimize edge effects. In an embodiment, an overlap of approximately1 degree is employed. It may be noted that any suitable approach knownin the art may be employed for stitching together the image slices.

In an embodiment, in order to reduce the effect of cargo motion, thesource pulsing frequency is increased approximately in proportion to thenumber fanlets. For example, in a mobile application, the pulsingfrequency is about 100 Hz. If the number of fanlets is 3, the frequencywould be increased to 300 Hz. In an embodiment, the smallest number offanlets is produced by dividing the corresponding fan beam in half;however this does not provide a significant reduction in scatter. Byincreasing the number of fanlets, which is achieved by decreasing theangular range of each fanlet, scatter radiation is decreased. However,an increased number of fanlets can only be obtained by proportionatelyincreasing the pulsing frequency for a pulsed Linac source.

In an embodiment, a typical angular range for a fan beam for a scanneris approximately 60 degrees. In an embodiment, the angular range of afanlet ranges from 1 degree to 30 degrees. In an embodiment, ten fanletsare employed, each having an angular range of 5 degrees. One of ordinaryskill in the art would appreciate that a fanlet has a considerablylarger angular range than a conventional pencil beam, which is on theorder of a fraction of a degree.

The X-ray dose to cargo and the environment does not increase, becausethe total number of X-rays is the same as compared to a standard X-rayscan. However, the scatter is reduced as there are fewer X-raysinspecting the cargo at any acquisition time relative to the primarybeam incident on the detectors.

For dual-energy scanning, the source may be either interlaced (meaningat a first pulse, a first energy, at a second pulse a second energy, andat an nth pulse an nth energy) or may contain both energies in the samepulse separated by a small time gap (>−100 ns). In this way, thefrequency is effectively increased by a factor of two. For example, in astandard system operating at 250 Hz, the source emission frequency maybeincreased to 375 Hz with a dual-energy per pulse, resulting in aneffective frequency of 750 Hz, enabling the use of three fanlets withsmall cargo motion effects.

In an embodiment, for interlaced dual-energy scanning, an odd number offanlets are generated so that the second energy is at the same fanletlocation in the following cycle to allow for dual-energy scanning ofevery vertical position. For example, in the case of three fanlets, inthe first cycle, the following pattern would be seen: Top Fanlet havingHigh Energy (HE), Center Fanlet having Low Energy (LE), and BottomFanlet having High Energy (HE). In the subsequent cycle, the followingpattern would be seen: Top Fanlet having Low Energy (LE), Center Fanlethaving High Energy (HE), and Bottom Fanlet having Low Energy (LE). Thus,in an embodiment, the first cycle is HE-LE-HE and the following cycle isLE-HE-LE, thereby allowing interlacing energy for the correspondingfanlet positions for consecutive cycles. It may be noted that if thenumber of fanlets is even, then the energy at each position would beeither LE or HE, and arrangements of LE-HE or HE-LE for the samevertical position will not be possible.

FIG. 3 illustrates a system comprising a CW source projectingcontinuously-moving fanlets, in a vertical motion, to scan cargo withreduced scatter, in accordance with another embodiment of the presentspecification. FIG. 3 illustrates an X-ray system comprising a CW X-raysource 310 and a detector array 320 scanning a cargo railcar 330.Collimator 340 represents a mechanism that produces a verticallycontinuously moving fan beam with an angular range smaller than theangular coverage of the railcar 330. The scanning mechanism issynchronized with a data acquisition module to start data collection atthe detector array 320 in position 350 and end data collection atposition 360 to cover an angular range of fanlet 370. In FIG. 3, the endposition 360 constitutes the start position of the next acquisitioncycle. The data collection continues in similar fashion until the fullvertical extent of the cargo is covered by the “individual” fanlets. Asin the pulse-source embodiment shown in FIG. 2, the scatter is reducedby using the CW source 310. It may be noted that the operation of thesystem remains the same regardless of whether the source is pulsed orCW. While a pulsed high energy x-ray source produces a pulse of a fewmicroseconds separated by few milliseconds, a CW source continuouslyproduces X-rays.

FIG. 4 is an exemplary illustration in which the imaging system of thepresent specification is used for scanning an ANSI 42.46 standardpenetration phantom object. As shown in FIG. 4, an ANSI 42.46penetration phantom object 401 is placed inside a rail-cargo 405. TheANSI 42.46 standard penetration phantom object 401 is used for assessingthe penetration capability of high-energy radiographic systems. Saidobject 401 comprises a rectilinear iron block 406 having a length and awidth of at least 60 cm each; and an iron block 404 of an approximaterhomboidal shape placed behind the rectilinear block 406. The thicknessof the rhomboidal block 406 is approximately 20% of the thickness of therectilinear block 406. In the testing procedure shown in FIG. 4, thephantom object 401 is placed at the center of a rail-cargo container 405tilted towards the X-ray source 402. An array of X-ray detectors 403 isset up to detect the X-rays transmitted through the object 401. Asuccessful ANSI test of penetration for an X-ray system is based onassessing the capability of that X-ray system in determining thedirection in which a tip 407 of the rhomboidal object 406 points in thecaptured image.

FIG. 5 illustrates exemplary simulated images for ANSI 42.46 penetrationphantom objects obtained with a full fan beam of X-rays and with the useof multiple fanlets via the imaging system described in FIG. 4, inaccordance with an embodiment of the present specification. Image 510 isformed by irradiating the phantom object (such as object 401 shown inFIG. 4) comprising a rectilinear object coupled with a rhomboidal shapedobject, with a full fan beam. As can be seen, the image quality of image510 is poor as it is difficult to distinguish the rhomboidal shapedobject 502 within rectilinear object 501 in this image. Image 520 isobtained by irradiating the phantom object (such as object 401 shown inFIG. 4) by using multiple fanlets of X-rays such as described withreference to FIG. 4. Using multiple fanlets, the image contrast isimproved as less scatter is measured. As can be seen, the image qualityof image 520 is better as the rhomboidal shaped object 502 withinrectilinear object 501 is better visible as compared to the image 510.Image 530 is obtained by irradiating the phantom object (such as object401 shown in FIG. 4) by using a larger number of fanlets of X-rays thanused to obtain image 520. By using a larger number of fanlets, even alower number of scattered X-rays are detected. As can be seen from thefigure, the quality of image 530 is better than that of image 520 as therhomboidal shaped object 502 within rectilinear object 501 is mostclearly visible in image 530.

The production of vertically moving fanlets of X-rays requires a systemfor projecting an X-ray beam with an angular range smaller than theangular coverage of the object being inspected. In one embodiment, thesystem comprises a radiation source that emits radiation at an emissionrate (R_(e)) and a conveyor that moves an object through the system at aconveyor rate (R_(c)), where the time (T_(f)) for a fanlet to traversethe object is preferably equal to the time for a single radiation pulse.In such a case, the total amount of time for a set of fanlets (which,when combined, cover the entire angular range encompassing the object)to be emitted is equal to times the total number of fanlets (N_(f)):T_(f)*N_(f). That total time, when multiplied by the conveyor rate(R_(c)), should preferably be equal to or less than a detector width(D_(w)), thereby insuring no portion of the object is missed. Therefore:

T_(f)*N_(f)*R_(c)≦D_(w), where T_(f) is the time for one fanlet, N_(f)is the total number of fanlets, R_(c) is the conveyor speed, and D_(w)is the detector width. Various embodiments for producingvertically-translated fanlets are described below.

FIG. 6A illustrates a mechanism comprising multiple actuators connectedto beam attenuators to produce vertically-moved fanlets, in accordancewith a preferred embodiment of the present specification. A plurality ofactuators 610 connect to a plurality of beam attenuators 630 throughsteel push/pull drive rods 620. The actuators 610 arecomputer-controlled to move the beam attenuators 630 to attenuate thebeam to project vertically moved fanlets, as described in more detail inFIG. 6B. In an embodiment, the actuators 610 are rotary actuators forobtaining a fast response time for scanning fast moving objects. Inalternate embodiments for deep scanning which includes scanning slowmoving or stationary objects, other types of actuators such as pneumaticactuators may be used.

In an embodiment, for performing a deep scan, a single fanlet having anangular range sufficient to cover the object's area of interest is used.In cases where a large part of a cargo being scanned is highlyattenuating, and scanning the same at a low speed is possible, X-rayfanlets such as described above are used to scan the cargo. However, thespeed of scan is maintained lower than that used for scanning a fastmoving cargo. In an embodiment, the number of fanlets used for scanningthe cargo at a slow speed is greater than that used for scanning a fastmoving cargo.

For example, and by way of example only, at a pulsing frequency of 1KHz, a Linac source produces 1 X-ray pulse every 1 millisecond (1/1000Hz=1 ms). While scanning an object moving at 3.6 km/h (or 1 mm in 1 msor 1 mm per pulse), by using a detector having a width of 10 mm, theentire object is covered by the X-rays because the detector is widerthan the distance moved by the object per pulse. Hence, the maximumnumber of fanlets that can be used to scan the object without missingany part of the object is 10, as it takes 1 ms per fanlet, which ifmultiplied by 10 fanlets =10 ms, meaning 10 mm of distance travelled bythe object, which is equal to the detector width. However, if the numberof fanlets is increased, for example to 20 fanlets, the time it wouldtake the fanlets to cover the object would be 20 ms, which means theobject also moves by 20 mm. Since the detector width is only 10 mm, apart of the object would be missed by the X-rays. However, if the speedof the object is lowered to 1.8 km/h, the object moves 10 mm in 20 ms,thereby allowing every part of the object to be scanned. Accordingly, inone embodiment, the system monitors whether the total fanlet time, whenmultiplied by the conveyor rate (R_(c)), is greater than a detectorwidth (D_(m)). If the system determines that it is, the conveyor rate is(R_(c)) is decreased to a rate sufficient to insure that the total time,when multiplied by the conveyor rate (R_(c)), is equal to or less than adetector width (D_(w)).

FIG. 6B is a block diagram illustrating various attenuatorconfigurations in the mechanism to produce vertically-moved fanletsshown in FIG. 6A. As shown in FIG. 6B, a vertical collimator 640 iscoupled with a plurality of beam attenuators 630 a, 630 b, . . . , 630n, which in turn are connected to a plurality of actuators (not shown inFIG. 6B) as shown in FIG. 6A. The vertical collimator 640 projects a fanbeam that covers the complete vertical extent of the object beingscanned. The plurality of attenuators 630 a, 630 b, . . . , 630 n may becontrolled by means of the rods 620 coupled with actuators 610, to movein and out of the projected beam to project X-ray fanlets that movevertically with respect to the object being scanned. In theconfiguration 650, attenuators 630 b, 630 c and 630 d are moved into thebeam to attenuate the beam, while attenuator 630 a stays out of the beamto project a fanlet over an upper part of the object being scanned. Inthe configuration 660 attenuators 630 a, 630 c and 630 d are moved intothe beam to attenuate the beam, while attenuator 630 b stays out of thebeam to project a fanlet over an upper middle part of the object beingscanned. In the configuration 670 attenuators 630 a, 630 b and 630 d aremoved into the beam to attenuate the beam, while attenuator 630 c staysout of the beam to project a fanlet over a lower middle part of theobject being scanned. In the configuration 680 attenuators 630 a, 630 band 630 c are moved into the beam to attenuate the beam, whileattenuator 630 d stays out of the beam to project a fanlet over a lowerpart of the object being scanned. Hence, the fanlet is moved to projectX-rays over different parts of the object being scanned by moving anattenuator out of the X-ray beam being projected. The movement of theattenuators as described provides vertically moving X-ray fanlets. Invarious embodiments, the beam attenuators 630 a, 630 b, . . . , 630 nare made of high-density materials such as but not limited to lead ortungsten.

In another embodiment X-ray fanlets may be moved vertically with respectto an object being scanned by means of a helical profile aperture formedon a rotating cylinder. FIG. 7 illustrates an exemplary design of aspin-roll chopper being used for moving X-ray fanlets vertically withrespect to an object being scanned, in accordance with an alternateembodiment of the present specification. The spin-roll chopper isdescribed in U.S. Pat. No. 9,058,909 B2, which is incorporated herein byreference in its entirety. The rotation of the spin roll/beam chopperprovides a vertically moving fanlet of constant size and velocity.

Beam chopper 702 is, in one embodiment, fabricated in the form of acylinder made of a material that highly attenuates X-rays. Beam chopper702 comprises helical chopper slits 704. The cylindrical shape enablesthe beam chopper 702 to rotate about a Z-axis 703 and along with thehelical apertures 704, create a spin-roll motion, which provides aneffective vertically moving aperture 704 that may project avertically-moving fanlet of X-rays onto an object being scanned. In oneembodiment, slits 704 are wide enough to allow a fanlet beam to beprojected, as required by the system of present specification. It may benoted that narrow slits would produce a pencil beam and not a fan orfanlet beam.

FIG. 8a shows an exemplary mechanism for generating moving fanlets,according to another alternate embodiment of the present specification.Referring to FIG. 8a rotating mechanism 800 comprises a wheel 801 withthree slits 802, 803 and 804, which are in the shape of an arc or apartial circle. In one embodiment, the wheel is made of a materialhighly attenuating for X-rays, such as lead or tungsten. Wheel 801further comprises a vertical collimator 805. In operation, as the wheelis rotated, the intersection of a slit 802 and the vertical collimator805 results in the blocking of the radiation from the slit, except for asection 806 a that projects a fanlet. In one embodiment, the width ofthe slit is configured to produce the desired fanlet angular extent. Inone embodiment, the rotating frequency of the wheel is determined basedon the fanlet width and linac pulsing frequency. The wheel rotation issynchronized with the linac pulsing frequency to generate fanlets withlittle overlap and cover the cargo extent in one cycle.

FIGS. 8b, 8c and 8d are a series of figures illustrating variouspositions of the wheel to indicate how the fanlets are produced and moveto cover the extent of an object being scanned. Referring to FIGS. 8b,8c and 8d , along with FIG. 8a , position 810 shows the fanlet 806 a inthe upper most location. When wheel 801 is rotated in a counterclockwisedirection, the fanlet 806 b moves downwards as shown by position 820 inFIG. 8b . One of ordinary skill in the art would appreciate that thewheel may be rotated in clockwise direction as well. Thus, with furtherrotation after position 820, the fanlet 806 c moves further down asshown in position 830 in FIG. 8c . When the fanlet exits the lowestposition, the next slit 803 in the wheel projects the upper fanlet 807.This is shown as position 840 in FIG. 8d . The cycles of rotation arerepeated until the complete object is scanned.

It may be noted that while the utilization of fanlets for scanningreduce the scatter, but there is still some scatter produced by thecargo interacting with the x-ray beam within the fanlet. Therefore inone embodiment, the system of the present specification measures thescatter with the detectors outside the fanlet and uses this measurementto estimate the scatter in the fanlet. The estimated scatter is thensubtracted from the transmission image data to increase contrast of theresultant image.

One of ordinary skill in the art would appreciate that even with theincreased penetration provided by the embodiments of the presentspecification, there would be dark alarms that may require manualinspection which is labor intensive. Therefore, in another embodiment,the present specification describes a method for scanning an object thatemploys a two-step process to further reduce dark alarms. This processis illustrated by means of a flow chart in FIG. 9.

Referring to FIG. 9, in the primary scan 901, a truck or cargo containeris scanned with a standard fan beam or fanlets of single or multi-energyhigh-energy radiation, where the transmitted radiation is measured withan array of detectors. In an embodiment, the truck or cargo container isscanned through a complete cycle, wherein a complete cycle is a scan ofthe vertical extent of the object under inspection using a standard fanbeam having an angular range or a plurality of fanlets having a totalangular range of a standard fan beam, as described above. Thus, in anembodiment, the fanlet, via collimator mechanics, is translatedvertically to cover the angular spread of the object in a completecycle. A pulsed linac X-ray source and a data acquisition system aresynchronized with the moving collimator in such a way that the image ofthe object is acquired at intervals, where in one cycle the fanletscover a slice of the object with no gaps and, optionally, a minimaloverlap. The image from each fanlet is then combined to produce a sliceimage.

The transmission information is analyzed in step 902 to determine areasof dark alarm. If no areas of dark alarm are found (903), then thetransmission image is analyzed to determine the presence of contrabandand other items of interest, as shown in 909.

If one or more areas of the image are not penetrated by the beam (darkalarm), the areas are subjected to a secondary scan, as shown in step903. In the secondary scan, a horizontal collimator is adjusted to onlycover the vertical extent of the dark area, and suspect areas, if any.This is shown in 904. The container is then repositioned to allow thelocation of suspect area to be rescanned. In one embodiment, theradiation source is tilted to align with the center of dark area, asshown in 905. In one embodiment, the rescan is preferably performed at alower speed than the primary scan, such as for example at 1/40^(th) ofthe standard scanning speed. This is shown in 906.

In one embodiment of the system, the source and detectors are mounted ona gantry that allows repositioning the system and scanning any part ofthe object with a wide range of speeds. Optionally, the source is tiltedin such a way that the beam center line is aligned with the center ofthe dark areas to increase the beam intensity, since the Bremsstrahlungx-rays are more intense.

The reduction of the vertical extent by suitably using a collimatorprevents scatter from other areas of the container and increasespenetration. It may be noted that scatter reduction also helps improvingmaterial separation with dual-energy beams as the single-energy imagesare cleaner from the scatter that distorts the x-ray spectra. The lowerscanning speed further allows for improved statistical accuracy and alsoincreases penetration.

Thereafter, the scanning system examines the transmission image again tocheck if there are any more dark alarms, as shown in 907. If more darkalarms are found in the scan image, a rescan is performed again, byrepeating the steps 904, 905 and 906. This process continues until alldark alarms are resolved.

When there are no more dark alarms, the rescanned sections of the imageare integrated into the original image of the object, as shown in 908.This is done, in one embodiment, by replacing the original sections ofthe image with corresponding rescanned sections. The transmission imageis then analyzed to determine the presence of contraband and other itemsof interest, as shown in 909.

Another motivation for the secondary scan, in addition to clear darkalarms, is to clear automated high-Z alarms. It may be noted that thesystem of present specification uses automated programs to generatealarms when a high Z material is detected. This system and method ofautomatically generating alarms when a high Z material is detected isdescribed in U.S. patent application Ser. No. 14/104,625, entitled“Systems and Methods for Automated, Rapid Detection of High AtomicNumber Materials” and filed by the applicant of the presentspecification, which is incorporated herein by reference in itsentirety.

It may be noted that the method for automatically detecting high Zmaterials employs attenuation information from the segmented objects andsurrounding background. Therefore, rescanning suspect objects with lowerscatter can resolve the alarm, as there is an improved single- anddual-energy contrast to reduce the need for active interrogation. Thus,in one embodiment, the system of present specification employs therescan approach described above with reference to FIG. 9, to clearautomated high Z alarms in a manner similar to clearance of dark alarms.In one embodiment, additional improvement is obtained by another scanperformed at a 10-20° angle to allow for a different view of the cargothat would have a different set of superimposing objects. One ofordinary skill in the art would appreciate that the requirement ofconfirming an alarm in all stages of scan would result in an even lowerfalse-alarm rate. Those skilled in the art would also appreciate thatsecondary inspection may be applied not only to high Z materials, butmay be extended to other objects of interest as well, such as suspectedcontraband including explosives, firearms, drugs, etc.

In one embodiment, the X-ray source may be replaced with a neutronsource. It may be noted that when the x-ray source is replaced with aneutron source, the detectors are replaced with neutron detectors andthe collimators are replaced with neutron-attenuating materials insteadof lead. However, the operation of the system remains the same.

In the description and claims of the application, each of the words“comprise” “include” and “have”, and forms thereof, are not necessarilylimited to members in a list with which the words may be associated.

The above examples are merely illustrative of the many applications ofthe system and method of present specification. Although only a fewembodiments of the present specification have been described herein, itshould be understood that the present specification might be embodied inmany other specific forms without departing from the spirit or scope ofthe specification. Therefore, the present examples and embodiments areto be considered as illustrative and not restrictive, and thespecification may be modified within the scope of the appended claims.

We claim:
 1. An X-ray detection system configured to provide forincreased penetration of an object, comprising: an X-ray source forgenerating an X-ray beam in an inspection volume; a conveyor for movingthe object through the inspection volume; a collimator positionedbetween the X-ray source and the object, wherein the collimator isconfigured to receive the X-ray beam and produce one or more fanletsfrom the X-ray beam, wherein each fanlet comprises a vertically movingfan beam having an angular range greater than 1 degree but smaller thanthe angular coverage of the object; a detector array opposing said X-raysource and positioned within the inspection volume for detecting the oneor more fanlets projected on the object; a controller configured tosynchronize the X-ray source and the collimator and collect image slicesfrom the detector array corresponding to each of the one more fanlets;and a processing unit for combining the image slices collected into acomposite image.
 2. The system of claim 1 wherein the X-ray source is apulsed X-ray source.
 3. The system of claim 2 wherein the X-ray sourceproduces dual-energy beams.
 4. The system of claim 3 wherein thedual-energy beams are interlaced.
 5. The system of claim 2 wherein theX-ray source produces X-ray pulses comprising low and high energy X-raybeams separated in time.
 6. The system of claim 1 wherein the controlleris configured to control the conveyor such that a total time for the oneor more fanlets multiplied by a rate of speed of the conveyor is equalto or less than a width of a detector in the detector array.
 7. Thesystem of claim 1 wherein the collimator is configured to generate anoverlap between the one or more fanlets of approximately 1 degree. 8.The system of claim 1 wherein the X-ray source is a CW X-ray source. 9.The system of claim 1 wherein the collimator for producing the one ormore fanlets comprises a plurality of controlled fast actuators coupledwith beam attenuators to shape the X-ray beam.
 10. The system of claim 1wherein the collimator for producing the one or more fanlets comprises abeam chopper.
 11. The system of claim 1 wherein the collimator forproducing the one or more fanlets comprises a rotating wheel with slitsdesigned to produce the vertically moving one or more fanlets.
 12. AnX-ray detection method comprising: irradiating an object with more thanone X-ray fanlet, wherein each X-ray fanlet comprises a verticallymoving fan beam having an angular range greater than 1 degree butsmaller than the angular coverage of the object and wherein each X-rayfanlet is produced by using a collimator for collimating an X-ray beamgenerated by an X-ray source; synchronizing the X-ray beam and the morethan one fanlet; detecting the more than one fanlet irradiating theobject; collecting image slices from the detector array corresponding toa complete scan cycle of the more than one fanlet; and processing theimage slices and combining the image slices into a composite image. 13.The method of claim 12 further comprising adjusting a beam intensity andenergy of each of the more than one fanlets based on signals detectedfrom a previous fanlet at a same vertical position with respect to theobject to generate a control output, wherein the control output is usedto control the X-ray detection method.
 14. The method of claim 12wherein the X-ray source is a pulsed X-ray source.
 15. The method ofclaim 12 wherein the X-ray source produces dual-energy beams.
 16. Themethod of claim 12 wherein the dual-energy beams are interlaced.
 17. Themethod of claim 12 wherein the X-ray source produces X-ray pulsescomprising low and high energy X-ray beams separated in time.
 18. Themethod of claim 12 wherein the collimator is configured to generate anoverlap between the one or more fanlets at every position with respectto a surface area of the object.
 19. The method of claim 12 wherein thecollimator comprises a spinning cylinder with a helical aperture. 20.The method of claim 12 wherein the collimator comprises a plurality ofcontrolled fast actuators coupled with beam attenuators to shape theX-ray beam.
 21. The method of claim 12 wherein an energy of each of themore than one fanlet is adjusted at a same fanlet location in afollowing cycle to allow for interlaced dual-energy scanning of everyvertical position.
 22. The method of claim 12 wherein the X-ray sourceis a CW X-ray source.
 23. A method for operating a scanning system,wherein said scanning system comprises an X-ray source, an array ofdetectors, and a processor to process and analyze image data, the methodcomprising: generating a first X-ray beam in order to conduct a firstscan to produce an image of the object being scanned; determining areasin said image data that require a more detailed inspection; configuringa collimator to limit a second X-ray beam such that, upon emission ofthe second X-ray beam, the collimator emits a plurality of fanlets,wherein each fanlet has an angular range that is less than an angularrange covering an object but greater than 1 degree; and moving theobject relative to the X-ray source and the array of detectors toperform a second scan on the areas.
 24. The method of claim 23 whereinsaid areas represent a lack of penetration by the first X-ray beamduring said first scan.
 25. The method of claim 23 wherein said areasrepresent items of interest or alarm such as explosive, firearms, drugsor contraband.
 26. The method of claim 23 wherein the X-ray source andarray of detectors are mounted on a gantry.
 27. The method of claim 23wherein the collimator comprises a plurality of controlled actuatorscoupled with beam attenuators to shape the second X-ray beam.
 28. Themethod of claim 23 wherein the collimator comprises two verticallycontrolled attenuators to inspect only said areas.
 29. The method ofclaim 23 wherein a scan of said areas using said plurality of fanlets isperformed at a lower speed compared to a speed of a scan using the firstX-ray beam.
 30. The method of claim 23 further comprising, replacing theareas generated by a scan using the first X-ray beam with images of theareas generated by a scan using the plurality of fanlets.